Biomedical subjects
R Naidu
Publications and source records attributed to R Naidu.
Identification of components of male-produced pheromone of coffee white stemborer, Xylotrechus quadripes.
The coffee white stem borer, Xylotrechus quadripes Chevrolat (Coleoptera: Cerambycidae), is the foremost pest of arabica coffee in India, Sri Lanka, China, Vietnam, and Thailand. Previous work showed that female beetles were attracted to traps baited with male beetles. Analyses of volatiles from male X. quadripes of Indian origin by gas chromatography (GC) linked to electroantennographic (EAG) recording from a female beetle antenna showed three male-specific components comprising more than 90% of the volatiles, two of which elicited EAG responses. The major EAG-active component was produced at up to 2 microg hr(-1) insect(-1) and was identified as (S)-2-hydroxy-3-decanone (I) by comparison of GC data, and mass (MS), infrared, and nuclear magnetic resonance (NMR) spectra with those of synthetic standards. The second component was identified as 3-hydroxy-2-decanone (II) produced in part by isomerization of I under the conditions of the GC analysis, although the NMR spectrum suggested it is naturally produced at up to 7% of I. The minor component that elicited an EAG response, present at 7% of the amount of I, was identified as (S,S)-2,3-dihydroxyoctane (III) from GC and MS data. 2-Hydroxy-3-octanone (0.2-0.5% of I), 2,3-decanedione (2% of I), 2-phenylethanol (3% of I), and octanoic acid (4% of I) were also identified in volatiles from male beetles. A general, stereospecific synthetic route to the enantiomers of 2-hydroxy-3-alkanones from the enantiomers of ethyl lactate was developed. The enantiomers of III were synthesized from (E)-2-octene by Sharpless asymmetric dihydroxylation. (S)-(I) was attractive to male X. quadripes in laboratory bioassays, but addition of (S,RS)-(III) at 10% of I reduced attractiveness. In field trials carried out in India with sticky, cross-vane traps, (S)- and (RS)-(I) attracted male X. quadripes and addition of (S,S)-(III) at 10% of I reduced attractiveness. Significant numbers of female Demonax balyi Pascoe (Coleoptera: Cerambycidae) were sometimes caught in traps baited with (S)-(I) alone.
The oral health and treatment needs of schoolchildren in Trinidad and Tobago: findings of a national survey.
OBJECTIVE: To describe the oral health and treatment need of schoolchildren in Trinidad and Tobago. DESIGN AND METHOD: Cross-sectional survey using stratified cluster sampling. Participants were children in primary (aged 6-8 years) and secondary school (aged 12 and 15 years). Main outcome measures were DMFT/dmft, treatment need, and fluorosis. RESULTS: Examinations were completed on 1064 children. The dmft of the 6-8-year-olds was 2.54 (95% CI = 2.32, 2.76). For 12-year-olds, the DMFT was 0.61 (95% CI = 0.51, 0.71), whereas for 15-year-olds, the DMFT was 1.06 (95% CI = 0.87, 1.25). Most of the caries experience in 6-8-year-olds was from decayed teeth. Sixty-seven per cent of the sample (95% CI = 64%, 69%) had some type of treatment need. Most frequently occurring need was for fillings at 42% (95% CI = 40%, 44%) with 28% (95% CI = 26%, 31%) of the total sample needing two or more surface fillings, followed by fissure sealants at 33% (95% CI = 30%, 36%) and caries-arresting care at 12% (95% CI = 10%, 14%). Extraction of one or more teeth was needed in 13% (95% CI = 11%, 15%) of children. Rates of fluorosis were negligible. CONCLUSION: The caries experience of 12- and 15-year-old children were low but was high for schoolchildren aged 6-8 years, in terms of prevalence and severity. Effective oral health promotion strategies need to be implemented to improve the oral health of primary schoolchildren in Trinidad and Tobago.
Distribution and nature of arsenic along former railway corridors of South Australia.
Elevated concentrations of arsenic (As) have been detected in soils of former railway corridors in South Australia, Australia. Elevated As concentrations resulted from the long-term application of As-based herbicides to control grass growth along former railway corridors. A study of former railway corridors revealed considerable surface (0-10 cm) contamination with As (<20 to >1000 mg As kg-1). The distribution of As in soils was related with particle size fraction and iron (Fe) oxide content. Total As increased markedly with decreasing particle size; sand<<silt<clay, with increasing As concentration generally correlated with increasing Fe concentrations (R2=0.57). A sequential fractionation of soils collected from selected sites showed that As was primarily associated with the amorphous and crystalline Fe and Al oxide materials. Solid phase speciation of As-contaminated soil indicated that arsenate (AsV) was the dominant As species present in the soil. However, in some soils, arsenite (AsIII) composed up to 40% of the total As present. The reasons for the presence of AsIII under alkaline and aerobic conditions are unclear.
Use of low-cost biological wastes and vermiculite for removal of chromium from tannery effluent.
Biological wastes (sawdust, rice husk, coirpith and charcoal) and a naturally occurring mineral (vermiculite) have been tested for their effectiveness in removing Cr from tannery effluent through batch and column experiments. The adsorption capacities of the substrates were also evaluated using isotherm tests and computing distribution co-efficient. The sawdust exhibited a higher adsorption capacity (k = 1482 mgkg(-1)), followed by coirpith (k = 159 mgkg(-1)). The biosorbent and mineral vermiculite in columns were found very effective in removing Cr from tannery effluent. About 94% removal of Cr was achieved by a column of coirpith, and equally (93%) by a column containing a mixture of coirpith and vermiculite. This study showed that biological wastes are potential adsorbents of Cr, which could be successfully used to reduce the Cr concentrations in tannery effluent.
Algal degradation of a known endocrine disrupting insecticide, alpha-endosulfan, and its metabolite, endosulfan sulfate, in liquid medium and soil.
The role of algae in the persistence, transformation, and bioremediation of two endocrine disrupting chemicals, alpha-endosulfan (a cyclodiene insecticide) and its oxidation product endosulfan sulfate, in soil (incubated under light or in darkness) and a liquid medium was examined. Incubation of soil under light dramatically decreased the persistence of alpha-endosulfan and enhanced its transformation to endosulfan sulfate, over that of dark-incubated soil samples, under both nonflooded and flooded conditions. This enhanced degradation of soil-applied alpha-endosulfan was associated with profuse growth of indigenous phototrophic organisms such as algae in soil incubated under light. Inoculation of soil with green algae, Chlorococcum sp. or Scenedesmus sp., further enhanced the degradation of alpha-endosulfan. The role of algae in alpha-endosulfan degradation was convincingly demonstrated when these algae degraded alpha-endosulfan to endosulfan sulfate, the major metabolite, and endosulfan ether, a minor metabolite, in a defined liquid medium. When a high density of the algal inoculum was used, both metabolites appeared to undergo further degradation as evident from their accumulation only in small amounts and the appearance of an endosulfan-derived aldehyde. Interestingly, beta-endosulfan was detected during degradation of alpha-endosulfan by high density algal cultures. These algae were also capable of degrading endosulfan sulfate but to a lesser extent than alpha-endosulfan. Evidence suggested that both alpha-endosulfan and endosulfan sulfate were immediately sorbed by the algae from the medium, which then effected their degradation. Biosorption, coupled with their biotransformation ability, especially at a high inoculum density, makes algae effective candidates for remediation of alpha-endosulfan-polluted environments.
Sorption-desorption of fenamiphos in surfactant-modified clays.
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Microbial degradation of illicit drugs, their precursors, and manufacturing by-products: implications for clandestine drug laboratory investigation and environmental assessment.
Chemicals associated with clandestine drug laboratories are often disposed of covertly into soil, sewerage systems, or public waste management facilities. There are two significant issues relating to such dumps of materials; they might contain valuable evidence as to drug manufacture, and they might be a source of pollution. This study presents initial findings in relation to the impact microorganisms from environmental sources have upon drugs, their precursors, and manufacturing by-products. The aim of this study was to identify which chemicals associated with clandestine drug laboratories persist in the environment in order to allow forensic drug chemists to link discarded residues with the method of manufacture, and to allow the environmental impact of clandestine drug laboratories to be assessed accurately. When exposed to soil microorganisms, phenyl-2-propanone (P2P) was rapidly metabolized into mixtures of 1-phenyl-2-propanol, 1-phenyl-1,2-propanedione, 1-hydroxy-1-phenyl-2-propanone, 2-hydroxy-1-phenyl-1-propanone, and the two diastereoisomers of 1-phenyl-1,2-propanediol. On the other hand, when exposed under the same conditions, methylamphetamine sulphate (MAS) remained virtually unchanged. Implications relating to evidence gathering for forensic purposes and to environmental assessment of clandestine drug laboratories are discussed.
Bioavailability of an organophosphorus pesticide, fenamiphos, sorbed on an organo clay.
Hydrolysis of an insecticide/nematicide, fenamiphos [ethyl-3-methyl-4-(methylthio)phenyl-(1-methylethyl)phosphoramidate], immobilized through sorption by cetyltrimethylammonium-exchanged montmorillonite (CTMA-clay) by a soil bacterium, Brevibacterium sp., was examined. X-ray diffraction analysis, infrared spectra, and a negative electrophoretic mobility strongly indicated that fenamiphos was intercalated within the bacterially inaccessible interlayer spaces of CTMA-clay. The bacterium hydrolyzed, within 24 h, 82% of the fenamiphos sorbed by the CTMA-clay complex. There was a concomitant accumulation of hydrolysis product, fenamiphos phenol, in nearly stoichiometric amounts. During the same period, in abiotic (uninoculated) controls, 4.6% of the sorbed insecticide was released into the aqueous phase as compared to 6.0% of the sorbed fenamiphos in another abiotic control where activated carbon, a sink for desorbed fenamiphos, was present. Thus, within 24 h, the bacterium hydrolyzed 77% more fenamiphos sorbed by organo clay than the amounts desorbed in abiotic controls. Such rapid degradation of an intercalated pesticide by a bacterium has not been reported before. Evidence indicated that extracellular enzymes produced by the bacterium rapidly hydrolyzed the nondesorbable fenamiphos, even when the enzyme itself was sorbed. Fenamiphos strongly sorbed to an organo clay appears to be readily available for exceptionally rapid degradation by the bacterium.
Hydrolysis of fenamiphos and its oxidation products by a soil bacterium in pure culture, soil and water.
A bacterium, identified as Brevibacterium sp. MM1, readily hydrolysed fenamiphos, a widely used organophosphorus insecticide and its toxic oxides (fenamiphos sulfoxide, fenamiphos sulfone), which all contain a common P-O-C bond, in a mineral salts medium. The bacterium also hydrolysed fenamiphos and its oxides in soil and groundwater. Interestingly, fenamiphos phenol, fenamiphos sulfoxide phenol and fenamiphos sulfone phenol, formed during bacterial hydrolysis of fenamiphos and its oxides, persisted in the mineral salts medium, but were transitory in soil and groundwater due to their further metabolism by indigenous micro-organisms. The cell-free preparation (crude enzyme) of this bacterium was very effective in hydrolysing fenamiphos. This is the first report on exceptionally rapid hydrolysis of fenamiphos by a bacterium in pure cultures, soil and groundwater.
Chemistry of chromium in soils with emphasis on tannery waste sites.
Worldwide chromium contamination of soils has arisen predominantly from the common practice of land-based disposal of tannery wastes under the assumption that the dominant species in the tannery waste would be the thermodynamically stable Cr(III) species. However, significant levels of toxic Cr(VI) recently detected in surface water and groundwater in India, China, Australia, and elsewhere raise critical questions relating to current disposal criteria for Cr-containing wastes. It now appears that despite the thermodynamic stability of Cr(III), the presence of certain naturally occurring minerals, especially Mn oxides, can enhance oxidation of Cr(III) to Cr(VI) in the soil environment. This factor is of public concern because at high pH, Cr(VI) is bioavailable, and it is this form that is highly mobile and therefore poses the greatest risk of groundwater contamination. A review of the current literature indicates that extensive research has been performed on the speciation of Cr in soil, the effect of pH on soil solution concentrations of Cr(III) and Cr(VI), soil adsorption phenomenon of Cr species, redox reactions, and transformation of Cr(II) and Cr(VI) together with remediation strategies to decontaminate Cr-contaminated soils. Most of the studies were conducted using an uncontaminated soil artificially spiked with Cr, and very limited research has been conducted in the contaminated soil environment. Furthermore, studies on tannery waste contaminated soils are limited, and obviously a serious gap of knowledge exists in understanding the influence of long-term tannery waste contamination on Cr behavior in soil.
Effect of amphetamine precursors and by-products on soil enzymes of two urban soils.
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Toxicity issues associated with geogenic arsenic in the groundwater-soil-plant-human continuum.
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Toxicity of hexavalent chromium and its reduction by bacteria isolated from soil contaminated with tannery waste.
An Arthrobacter sp. and a Bacillus sp., isolated from a long-term tannery waste contaminated soil, were examined for their tolerance to hexavalent chromium [Cr(VI)] and their ability to reduce Cr(VI) to Cr(III), a detoxification process in cell suspensions and cell extracts. Both bacteria tolerated Cr(VI) at 100 mg/ml on a minimal salts agar medium supplemented with 0.5% glucose, but only Arthrobacter could grow in liquid medium at this concentration. Arthrobacter sp. could reduce Cr(VI) up to 50 microg/ml, while Bacillus sp. was not able to reduce Cr(VI) beyond 20 microg/ml. Arthrobacter sp. was distinctly superior to the Bacillus sp. in terms of their Cr(VI)-reducing ability and resistance to Cr(VI). Assays with permeabilized (treated with toluene or Triton X 100) cells and crude extracts demonstrated that the Cr(VI) reduction was mainly associated with the soluble protein fraction of the cell. Arthrobacter sp. has a great potential for bioremediation of Cr(VI)-containing waste.
Microbial activity and phospholipid fatty acid pattern in long-term tannery waste-contaminated soil.
We investigated the phospholipid fatty acid (PLFA) pattern and dehydrogenase activity (DHA) in soil samples from three sites (designated as low, medium, and high based on the level of chromium) in a long-term (25 years after last waste input) tannery waste-contaminated area rich in Cr. Soil samples, collected from different soil depths (0-100 cm), at each site were used in this study. In general, soil samples from all three contaminated sites had elevated pH, electrical conductivity, organic carbon (OC), total Cr, and hexavalent Cr [Cr(VI)]. The maximum total Cr concentration in surface soils (0-10 cm) at the highly contaminated site was 102 gkg(-1), with 4.6 mgkg(-1) present as the bioavailable water-soluble Cr. More than 50% of soluble Cr was in the form of Cr(VI) (2.7 mgkg(-1)). DHA (normalized to OC) was inhibited to a greater extent in soil samples from the highly contaminated site than in low- and medium-contaminated soil samples. PLFA analyses of surface soils indicated that there was a shift in PLFA patterns. PLFAs specific for bacteria (i15:0, a15:0, 15:0, i16:0, a17:0, and cy17:0) decreased significantly (P<0.01) with an increase in Cr contamination. Among the bacterial PLFAs, 15:0, i16:0 and a17:0 had a significant negative correlation with contamination including bioavailable Cr(VI) in soil solution. To our knowledge, this is the first report of alterations in the PLFA profile in soils due to long-term tannery waste pollution.
Changes in microbial properties associated with long-term arsenic and DDT contaminated soils at disused cattle dip sites.
This work examined the effect of long-term arsenic (As) and DDT contamination on soil microbial properties at 11 cattle dip sites in northern New South Wales, Australia. Total As in the surface (0-10 cm) soils from these sites ranged from 34 to 2941 mg As kg(-1) soil and hexane-extractable DDT concentrations ranged between 2.9 and 7673 mg DDT kg(-1) soil. The concentrations of water and oxalate-extractable As were positively correlated with total As. Oxalate-extractable As was more strongly correlated (r(2)=0.87) with total As than water-extractable As (r(2)=0.34). A weak positive relationship was observed between the level of nutrient (organic carbon and nitrogen) and microbial biomass C (r(2)=0.61 and 0.45, respectively). There was a highly significant difference between the microbial properties of polluted and unpolluted sites (P<0.001). In comparison to unpolluted soils, fungal counts, microbial biomass C, and respiration were dramatically reduced (P<0.05) in polluted soils. However, the bacterial population between polluted and unpolluted soils were not different (P<0.05). The results of this study suggested that (a) long-term contamination of soils adjacent to former cattle dipping sites by As and DDT adversely affected soil microbial properties with the fungal populations being the most sensitive and (b) there was little regeneration of microbiota despite 25 years of field ageing of the soils.
The acceptability of the use of sedation in the management of dental anxiety in children: views of dental students.
The aim of the present study was to determine the views of dental students concerning the acceptability of the use of sedation in the management of dentally anxious children. Dental students in Trinidad (n = 100) were asked to rate the acceptability of vignettes describing the management of a young teenager with dental anxiety. The vignettes varied systematically along two dimensions: nature of intervention for anxiety (sedation vs. the use of relaxation training and rewards) and outcome of the intervention (good vs. poor). Ratings of acceptability were made using a standardized questionnaire measure. The data were analysed using analysis of variance (ANOVA). There were significant main effects of nature of intervention (F = 5.54; P < 0.05) and outcome of intervention (F = 298.01; P < 0.001), though the students' year of study did not influence ratings. None of the interaction terms were significant. Sedation was viewed as a less acceptable intervention than relaxation and rewards. Interventions associated with good outcomes were seen as more acceptable than interventions associated with poor outcomes. It is concluded that dental students' perceptions of the acceptability of interventions for use with dentally anxious patients are related to the effectiveness of the intervention. Sedation, regardless of the outcome, is seen as less acceptable than the use of rewards and relaxation.
Arsenic in Australian environment: an overview.
The most common source of elevated As concentrations in the Australian environment are attributable to anthropogenic activities. Mining activities have contributed to the contamination of soil and water primarily in Western Australia and Victoria. However, other anthropogenic activities such as agriculture, forestry and industry have also contaminated soil and water at a localized scale. Currently there are over 1000 As contaminated sites previously used as cattle dips for eradicating cattle ticks. Although As contamination of the environment may be severe enough to limit plant growth there appears to be few other reports identifying the impacts of the contaminants on other organisms, such as fish, mammals and humans. In Australia the impacts of metal/metalloid contamination of the environment are often unnoticed or ignored. However, the impacts of elements such as As may pass unnoticed by the public or regulators due to the perception of the minimal impact a contaminant has on the environment. This paper presents an overview of As in the Australian environment including the sources of As contamination, soil, water and plant As content, and the pathways of exposure.